Sydney teenager shot 'execution style' while in bed dies in hospital

A Sydney teenage is "critical" after being shot in the head this morning.

A teenage boy shot in the head in his own bed while asleep early this morning in Sydney has died, police have confirmed.

The 15-year-old victim, Brayden Dillon, died in hospital after what has been described as an "execution style" attack in Sydney's south west. The incident is believed to be linked to another homicide, a stabbing in July last year, according to news.com.au.

Adam Abu-Mahmoud was stabbed to death after a brawl erupted two rival groups in Panania, southwest of the central city.

The Daily Telegraph reported Brayden was related to one of three people who were charged in relation to the murder of Abu-Mahmoud.

Police are investigating the circumstances surrounding the shooting that killed Brayden which occurred in Glenfield, south of Liverpool - but the possibility it was a revenge attack is being explored.

The gunman fled the scene and police say they say they are looking for a man aged between 18 and 20 who may be armed in connection with the incident.

The man police are hunting has a thin build, and was last seen wearing grey tracksuit pants, a navy blue hooded jacket and white joggers. It's believed he may be armed, and police warn he should not be approached.

Emergency services were called to a home on Moresby Avenue at about 6.10am and found a teenage boy with a gunshot wound to his head.

It is believed Brayden's mother confronted the attacker but locked herself in a bedroom when a pistol was brandished.

Detective Chief Inspector Mark Brett said it appeared to be a targeted attack.

His mother, stepfather and two young siblings were not injured but his mother was "extremely distressed," he said.

Talking to reporters today, Inspector Paul Kremer from Macquarie Fields police said the attacker went upstairs and "forced entry to the victim's room".

It is believed the boy was shot while still in bed asleep.

"At this stage the young person is extremely critical," Insp Kremer told media.

A one-year-old baby and a seven-year-old were also at home at the time.

Insp Kremer said it was "too early to say he knew" the shooter and it was linked to an earlier homicide, although the incident has been described as a "revenge attack".

The 15-year-old was treated at the scene by ambulance paramedics before being taken to Westmead Hospital where he died.